Range sensor and range image sensor

ABSTRACT

A signal charge collecting region is disposed inside a charge generating region so as to be surrounded by the charge generating region, and collects signal charges from the charge generating region. An unnecessary charge collecting region is disposed outside the charge generating region so as to surround the charge generating region, and collects unnecessary charges from the charge generating region. A transfer electrode is disposed between the signal charge collecting region and the charge generating region, and causes the signal charges from the charge generating region to flow into the signal charge collecting region in response to an input signal. An unnecessary charge collecting gate electrode is disposed between the unnecessary charge collecting region and the charge generating region, and causes the unnecessary charges from the charge generating region to flow into the unnecessary charge collecting region in response to an input signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priorities fromU.S. Provisional application Ser. No. 61/605,906 filed on Mar. 2, 2012,and Japanese Patent Application No. 2012-041317 filed on Feb. 28, 2012,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a range sensor and a range imagesensor.

2. Related Background Art

A TOF (Time-Of-Flight)-type range image sensor (range sensor) is known(see, for example, T. Y. Lee et al., “A 192×108 pixel ToF-3D imagesensor with single-tap concentric-gate demodulation pixels in 0.13 μmtechnology,” Proceedings of the 2011 IEEE International Electron DevicesMeeting, Dec. 5-8, 2011, pp. 8.7.1-8.7.4). The range image sensordescribed in this literature includes a charge generating regionconfigured to generate charges in response to incident light, a chargecollecting region disposed inside the charge generating region so as tobe surrounded by the charge generating region, a charge dischargingregion disposed outside the charge generating region so as to surroundthe charge generating region, an inside gate electrode disposed on thecharge generating region and configured to cause charges to flow fromthe charge generating region into the charge collecting region inresponse to an input signal, and an outside discharge gate electrodedisposed on the charge generating region and configured to cause chargesfrom the charge generating region into the charge discharging region inresponse to an input signal. Because of a potential difference appliedbetween the inside gate electrode and the outside discharge gateelectrode, a potential gradient is formed across regions immediatelybelow the inside gate electrode and the outside discharge gateelectrode. Because of this potential gradient, the charges generated inthe charge generating region migrate to the charge collecting region orcharge discharging region.

SUMMARY OF THE INVENTION

However, the range image sensor described in the literature has thefollowing problem.

When a potential gradient descending from the outside discharge gateelectrode side to the inside gate electrode side is formed, chargesmigrate to the charge collecting region. In this case, a potentialformed in the region immediately below the outside discharge gateelectrode has a gradient descending to the charge discharging region onthe charge discharging region side, and some of the charges generated inthe charge generating region migrate to the charge discharging region.Accordingly, a transfer efficiency of the charges to the chargecollecting region is deteriorated, and therefore an accuracy of distancedetection is also deteriorated. In particular, the outside dischargegate electrode is disposed on the charge generating region, is locatedoutside the inside gate electrode, and has a relatively large area, sothat it is easy for some of the charges generated in the chargegenerating region to migrate to the charge discharging region.

When a potential gradient descending from the inside gate electrode sideto the outside discharge gate electrode side is formed, charges migrateto the charge discharging region. In this case, the potential gradientformed in a region immediately below the inside gate electrode is agradient descending to the charge collecting region on the chargecollecting region side, and some of the charges generated in the chargegenerating region migrate to the charge collecting region. Accordingly,a transfer efficiency of the charges to the charge discharging region isdeteriorated, and charges resulting from background light (ambientlight) are not discharged and accumulate in the charge dischargingregion. When charges which should have been discharged are accumulatedin the charge discharging region, the accumulation capacity is saturatedbefore a signal is read out. As a result, the accuracy of distancedetection is deteriorated.

An object of the present invention is to provide a range sensor and arange image sensor which are capable of improving the accuracy ofdistance detection.

In an aspect, the present invention is a range sensor comprising: acharge generating region configured to generate charges in response toincident light; a signal charge collecting region disposed inside thecharge generating region so as to be surrounded by the charge generatingregion, and configured to collect signal charges from the chargegenerating region; an unnecessary charge collecting region disposedoutside the charge generating region so as to surround the chargegenerating region, and configured to collect unnecessary charges fromthe charge generating region; a photogate electrode disposed on thecharge generating region; a transfer electrode disposed between thesignal charge collecting region and the charge generating region, andconfigured to cause the signal charges from the charge generating regionto flow into the signal charge collecting region in response to an inputsignal; and an unnecessary charge collecting gate electrode disposedbetween the unnecessary charge collecting region and the chargegenerating region, and configured to cause the unnecessary charges inthe charge generating region to flow into the unnecessary chargecollecting region in response to an input signal.

In the present invention, the photogate electrode is disposed on thecharge generating region, the transfer electrode is disposed between thesignal charge collecting region and the charge generating region, andthe unnecessary charge collecting gate electrode is disposed between thecharge generating region and the unnecessary charge collecting region.When signal charges are transferred to the signal charge collectingregion, a potential gradient descending from the unnecessary chargecollecting gate electrode side to the transfer electrode side is formedacross regions immediately below the photogate electrode, the transferelectrode and the unnecessary charge collecting gate electrode.Accordingly, the charges generated in the charge generating region belowthe photogate electrode definitely migrate to the signal chargecollecting region, but find it difficult to migrate to the unnecessarycharge collecting region. As a result, the transfer efficiency of thesignal charges is improved. When unnecessary charges are transferred tothe unnecessary charge collecting region, a potential gradientdescending from the transfer electrode side to the unnecessary chargecollecting gate electrode side is formed across regions immediatelybelow the photogate electrodes, the transfer electrodes and theunnecessary charge collecting gate electrode. Accordingly, the chargesgenerated in the charge generating region below the photogate electrodedefinitely migrate to the unnecessary charge collecting region asunnecessary charges, but find it difficult to move to the signal chargecollecting region. As a result, the transfer efficiency of theunnecessary charges is improved. As a consequence, the present inventioncan improve the accuracy of distance detection.

The range sensor may be provided with a plurality of the chargegenerating regions, a plurality of the signal charge collecting regions,a plurality of the unnecessary charge collecting regions, a plurality ofthe photogate electrodes, a plurality of the transfer electrodes and aplurality of the unnecessary charge collecting gate electrodes, and theplurality of the transfer electrodes may be supplied respective chargetransfer signals having different phases. In this case, the plurality ofthe charge generating regions corresponds to one pixel, and the distanceis calculated based on outputs from the one pixel.

The adjacent unnecessary charge collecting regions may be formedintegrally with each other. In this case, the distance between theadjacent charge generating regions is shortened, and therefore a usageefficiency of the sensor area can be increased. As a result, a spatialresolution can be improved.

The plurality of the charge generating regions may be formed asspatially separated from each other. In this case, the unnecessarycharge collecting region is located between the adjacent chargegenerating regions, and therefore unnecessary charges definitely migrateto the unnecessary charge collecting region. Accordingly, the transferefficiency of the unnecessary charges can be further improved.

The adjacent charge generating regions may be formed integrally witheach other, and the adjacent photogate electrodes may be formedintegrally with each other. In this case, the charge generating regionis expanded with respect to a single charge collecting region, andtherefore there is an increase in the signal charges migrating to thecharge collecting region. Accordingly, the transfer efficiency of thesignal charges can be further improved.

The transfer electrode may be supplied a transfer signal which isintermittently given a phase shift at a predetermined timing. In thiscase, one charge generating region corresponds to one pixel, and thedistance is calculated based on outputs from the same pixel. For thisreason, this configuration can reduce the deviation in the calculationof the distance compared to a configuration in which a plurality of thecharge generating regions corresponds to one pixel. Furthermore, theusage efficiency of the sensor area can be increased, and the spatialresolution can be improved.

The photogate electrode, the transfer electrode and the unnecessarycharge collecting gate electrode may be concentrically disposed aroundthe signal charge collecting region in an order of the transferelectrode, the photogate electrode, and the unnecessary chargecollecting gate electrode from the signal charge collecting region side.The signal charge collecting region may be rectangular-shaped whenviewed in a plan view, and the photogate electrode, the transferelectrode, and the unnecessary charge collecting gate electrode may beapproximately polygonal loop-shaped. The signal charge collecting regionmay be circular-shaped when viewed in a plan view, and the photogateelectrode, the transfer electrode, and the unnecessary charge collectinggate electrode may be approximately circular loop-shaped.

In another aspect, the present invention is a range image sensor whichcomprises an imaging region including a plurality of units disposed in aone-dimensional or two-dimensional arrangement on a semiconductorsubstrate and which obtains a range image based on charge quantitiesoutput from the units, wherein each of the units is the aforementionedrange sensor.

According to the present invention, the accuracy of distance detectioncan be improved by improving the transfer efficiency of the signalcharges and unnecessary charges, as described above.

Adjacent two units out of the plurality of the units may constitute onepixel of the imaging region.

In any one unit out of the plurality of the units and a plurality ofunits adjacent the any one unit, the any one unit and one unit out ofthe plurality of the units may constitute one pixel of the imagingregion. In this case, the usage efficiency of the sensor area can beincreased, thereby improving the spatial resolution.

Each of the units may constitute one pixel of the imaging region. Inthis case, the distance is calculated based on outputs from the samepixel, and therefore the deviation in the calculation of the distancecan be reduced. The usage efficiency of the sensor area can beincreased, thereby improving the spatial resolution.

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not to beconsidered as limiting the present invention.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory diagram illustrating a configuration of adistance measuring device according to an embodiment.

FIG. 2 is a diagram for explaining a cross-sectional configuration of arange image sensor.

FIG. 3 is a schematic plan view of the range image sensor.

FIG. 4 is a schematic diagram for explaining a configuration of a pixelof the range image sensor.

FIG. 5 is a diagram illustrating a cross-sectional configuration alongline V-V in FIG. 4.

FIG. 6 is a diagram illustrating a potential profile, for explainingaccumulation and discharge operations of charge.

FIG. 7 is a diagram illustrating a potential profile, for explainingaccumulation and discharge operations of charge.

FIG. 8 is a schematic diagram for explaining a configuration of a pixel.

FIG. 9 is a timing chart of various signals.

FIG. 10 is a schematic diagram for explaining a configuration of a pixelof a range image sensor according to a modification example.

FIG. 11 is a schematic diagram for explaining a configuration of a pixelof a range image sensor according to a modification example.

FIG. 12 is a schematic diagram for explaining a configuration of a pixelof a range image sensor according to a modification example.

FIG. 13 is a schematic diagram for explaining a configuration of a pixelof a range image sensor according to a modification example.

FIG. 14 is a diagram illustrating a cross-sectional configuration alongline XIV-XIV in FIG. 13.

FIG. 15 is a timing chart of various signals.

FIG. 16 is a diagram illustrating a potential profile, for explaining anaccumulation operation of signal charges.

FIG. 17 is a diagram illustrating a potential profile, for explaining anaccumulation operation of signal charges.

FIG. 18 is a diagram illustrating a potential profile, for explaining adischarge operation of unnecessary charges.

FIG. 19 is a schematic diagram for explaining a configuration of a pixelof a range image sensor according to a modification example.

FIG. 20 is a timing chart of various signals.

FIG. 21 is a schematic diagram for explaining a configuration of a pixelof a range image sensor according to a modification example.

FIG. 22 is a diagram illustrating a cross-sectional configuration alongline XXII-XXII in FIG. 21.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will be described indetail below with reference to the accompanying drawings. In thedescription, the same elements or elements with the same functionalitywill be denoted by the same reference signs, without redundantdescription.

FIG. 1 is an explanatory diagram illustrating a configuration of adistance measuring device.

This distance measuring device is provided with a range image sensor 1,a light source 3 configured to emit near-infrared light, a drivingcircuit 4, a controlling circuit 2, and an arithmetic circuit 5. Thedriving circuit 4 supplies a pulse drive signal S_(P) to the lightsource 3. The controlling circuit 2 supplies detection gate signals S₁,S₂ synchronized with the pulse drive signal S_(P) to first and secondgate electrodes (TX1, TX2: cf. FIG. 4) included in each pixel of therange image sensor 1. The arithmetic circuit 5 calculates a distance toan object H, such as a pedestrian or the like, based on a signal d′(m,n) indicative of distance information read out from the first and secondsemiconductor regions (FD1, FD2: cf. FIG. 4) of the range image sensor1. The distance from the range image sensor 1 to the object H in ahorizontal direction D is set to d. The controlling circuit 2 alsooutputs a charge transfer signal S₃ described below.

The controlling circuit 2 inputs a pulse drive signal S_(P) to theswitch 4 b of the driving circuit 4. The light source 3 for projectionof light including an LED or a laser diode is connected to a powersource 4 a via the switch 4 b. When the pulse drive signal S_(P) isinput to the switch 4 b, a drive current having the same waveform as thepulse drive signal S_(P) is supplied to the light source 3, and thelight source 3 outputs pulsed light L_(P) as probe light for distancemeasurement. When the pulse light L_(P) is irradiated onto the object H,the pulse light is reflected from the object H. The reflected pulselight is incident into the range image sensor 1 as pulse light L_(D),and a pulse detection signal S_(D) is output.

The range image sensor 1 is disposed on a wiring board 10. The signald′(m, n) including distance information is output from each pixel of therange image sensor 1 via wiring of the wiring board 10.

The waveform of the pulse drive signal Sp is a rectangular wave havingperiod T. Assuming that a high level is “1” and a low level is “0,” thevoltage V(t) of the pulse drive signal S_(P) is given as the followingequations:

Pulse drive signal S_(P):

V(t)=1(in the case of 0<t<(T/2));

V(t)=0(in the case of (T/2)<t<T);

V(t+T)=V(t).

The waveforms of the detection gate signals S₁, S₂ are rectangular waveshaving period T. The voltage V(t) of the detection gate signals S₁, S₂is given as the following equations:

Detection gate signal S₁:

V(t)=1(in the case of 0<t<(T/2));

V(t)=0(in the case of (T/2)<t<T);

V(t+T)=V(t).

Detection gate signal S₂ (=inversion of S₁)):

V(t)=0(in the case of 0<t<(T/2));

V(t)=1(in the case of (T/2)<t<T);

V(t+T)=V(t).

The foregoing pulse signals S_(P), S₁, S₂, S_(D) all have pulse period(2×T_(P)). When the detection gate signal S₁ and the pulse detectionsignal S_(D) are all “1,” a charge quantity generated in the range imagesensor 1 is set to Q1. When the detection gate signal S₂ and the pulsedetection signal S_(D) are all “1,” a charge quantity generated in therange image sensor 1 is set to Q2.

A phase difference between the detection gate signal S₁ and the pulsedetection signal S_(D) is proportional to the charge quantity Q2generated in the range image sensor 1 in an overlap duration in whichthe detection gate signal S₂ and the pulse detection signal S_(D) are“1.” That is, the charge quantity Q2 is a charge quantity which isgenerated in the duration in which the logical AND of the detection gatesignal S₂ and the pulse detection signal S_(D) is “1.” When the totalcharge quantity generated within a single pixel is Q1+Q2 and thehalf-period pulse width of the pulse drive signal S_(P) is T_(P), thepulse detection signal S_(D) lags behind the pulse drive signal S_(P) byΔt=T_(P)×Q2/(Q1+Q2). The time of flight Δt of one light pulse is givenby Δt=2d/c, where d is the distance to the object and c the speed oflight. For this reason, when the two charge quantities (Q1, Q2) areoutput as a signal d′(m, n) having the distance information from aspecific pixel, the arithmetic circuit 5 calculates the distanced=(c×Δt)/2=c×T_(P)×Q2/(2×(Q1+Q2)) to the object H, based on the inputcharge quantities Q1, Q2 and the predetermined half-period pulse widthT_(P).

As described above, the arithmetic circuit 5 can calculate the distanced by separately reading out the charge quantities Q1, Q2. The foregoingpulses are repeatedly emitted and integral values thereof can be outputas respective charge quantities Q1, Q2.

The ratios of the charge quantity Q2 to the total charge quantitycorrespond to the above-described phase difference, that is, thedistance to the object H. The arithmetic circuit 5 calculates thedistance to the object H based on the phase difference. As describedabove, when the time difference corresponding to the phase difference isset to Δt, the distance d is preferably given by d=(c×Δt)/2, but anappropriate correction operation may be performed in addition thereto.For example, if an actual distance is different from the calculateddistance d, a factor β to correct the latter is preliminarily obtainedand the finally calculated distance d is obtained by multiplying thefactor β to the calculated distance d in a product after shipped.Another available correction is such that an ambient temperature ismeasured, an operation to correct the speed of light c is performed ifthe speed of light c differs depending upon the ambient temperature, andthen the distance calculation is performed. It is also possible topreliminarily store in a memory a relation between signals input intothe arithmetic circuit and actual distances, and determine the distanceby a lookup table method. The calculation method can be modifieddepending upon the sensor structure and the conventionally knowncalculation methods can be applied thereto.

FIG. 2 is a diagram for explaining a cross-sectional configuration ofthe range image sensor.

The range image sensor 1 is a front-illuminated type range image sensor,and has a semiconductor substrate 1A. Pulse light L_(D) is incidentthrough a light incident surface 1FT of the semiconductor substrate 1Ainto the range image sensor 1. The back surface 1BK of the range imagesensor 1 opposite the light incident surface 1FT is connected through anadhesive region AD to the wiring board 10. The adhesive region ADincludes an insulating adhesive and a filler. The range image sensor 1includes a light-shielding layer LI having an opening at a predeterminedlocation. The light-shielding layer LI is disposed on the front of thelight incident surface 1FT.

FIG. 3 is a schematic plan view of the range image sensor.

In the range image sensor 1, the semiconductor substrate 1A has animaging region 1B which includes a plurality of pixels P(m, n) which aredisposed in a two-dimensional arrangement. Each pixel P(m, n) outputstwo charge quantities (Q1, Q2) as the aforementioned signal d′(m, n)having the distance information. Each pixel P(m, n) functions as amicroscopic distance measuring sensor, and outputs the signal d′(m, n)based on the distance to the object H. Therefore, when light reflectedfrom the object H is focused on the imaging region 1B, a range image ofthe object as a collection of distance information to respective pointson the object H can be acquired. A single pixel P(m, n) functions as asingle range sensor.

FIG. 4 is a schematic diagram for explaining a configuration of a pixelin the range image sensor. FIG. 5 is a diagram illustrating across-sectional configuration along the line V-V in FIG. 4.

The range image sensor 1, as shown in FIG. 2, is provided with thesemiconductor substrate 1A having the light incident surface 1FT and theback surface 1BK opposed to each other. The semiconductor substrate 1Ahas a p-type first substrate region 1Aa located on the back surface 1BKside, and a p⁻-type second substrate region 1Ab located on the lightincident surface 1FT side. The second substrate region 1Ab has a higherimpurity concentration than the first substrate region 1Aa. Thesemiconductor substrate 1A may be acquired, for example, by growing ap⁻-type epitaxial layer on a p-type semiconductor substrate, the p⁻-typeepitaxial layer has a lower impurity concentration than thesemiconductor substrate.

In each pixel P(m, n), the range image sensor 1 is provided with aplurality of photogate electrodes (in the present embodiment, twophotogate electrodes) PG1, PG2, first and second gate electrodes TX1,TX2, a plurality of third gate electrodes (in the present embodiment,two third gate electrodes) TX3 ₁, TX3 ₂, first and second semiconductorregions FD1, FD2, and a plurality of third semiconductor regions (in thepresent embodiment, two third semiconductor regions) FD3 ₁, FD3 ₂.

The two photogate electrodes PG1, PG2 are provided through an insulatinglayer 1E on the light incident surface 1FT, and are arranged asspatially separated from each other. The first and third gate electrodesTX1, TX3 ₁ are provided through an insulating layer 1E on the lightincident surface 1FT, and are located adjacent to the photogateelectrode PG1. The second and third gate electrodes TX2, TX3 ₂ areprovided through an insulating layer 1E on the light incident surface1FT, and are located adjacent to the photogate electrode PG2.

The first and second semiconductor regions FD1, FD2 accumulaterespective charges flowing into regions immediately below thecorresponding gate electrodes TX1, TX2. In the present embodiment, thesemiconductor substrate 1A is comprised of Si, and the insulating layer1E is comprised of SiO₂.

Approximately polygonal loop-shaped openings LI1, LI2 are formed in thelight-shielding layer LI. These openings LI1, LI2 have a rectangularloop-shape. Light (reflected light from the object H) is incident uponthe semiconductor substrate 1A through the openings LI1, LI2 of thelight-shielding layer LI. Therefore, rectangular loop-shaped lightreceiving regions are defined in the semiconductor substrate 1A by theopenings LI1, LI2. The light-shielding layer LI is comprised of, forexample, metal such as aluminum.

The photogate electrodes PG1, PG2 are disposed to correspond to theopenings LI1, LI2. The shapes of the photogate electrodes PG1, PG2 alsocorrespond to those of the openings LI1, LI2, and are approximatelypolygonal loop shape when viewed in a plan view. In the presentembodiment, the photogate electrodes PG1, PG2 are rectangularloop-shaped. Although the photogate electrodes PG1, PG2 are comprised ofpolysilicon, they may be comprised of other materials.

The first semiconductor region FD1 is disposed inside the photogateelectrode PG1 so as to be surrounded by the photogate electrode PG1. Thefirst semiconductor region FD1 is arranged as spatially separated from aregion immediately below the photogate electrode PG1. That is, the firstsemiconductor region FD1 is disposed inside the light receiving regionso as to be surrounded by the light receiving region, and is arranged asspatially separated from the light receiving region.

The second semiconductor region FD2 is disposed inside the photogateelectrode PG2 so as to be surrounded by the photogate electrode PG2. Thesecond semiconductor region FD2 is arranged as spatially separated froma region immediately below the photogate electrode PG2. That is, thesecond semiconductor region FD2 is disposed inside the light receivingregion so as to be surrounded by the light receiving region, and isarranged as spatially separated from the light receiving region.

The first and second semiconductor regions FD1, FD2 are approximatelypolygon-shaped when viewed in a plan view. In the present embodiment,the first and second semiconductor regions FD1, FD2 are rectangle-shaped(in detail, square-shaped). The first and second semiconductor regionsFD1, FD2 function as signal charge collecting regions. The first andsecond semiconductor regions FD1, FD2 are regions comprised ofhigh-impurity concentration n-type semiconductors, and are floatingdiffusion regions.

The first gate electrode TX1 is disposed between the photogate electrodePG1 (light receiving region) and the first semiconductor region FD1. Thefirst gate electrode TX1 is located outside the first semiconductorregion FD1 so as to surround the first semiconductor region FD1, and isalso located inside the photogate electrode PG1 so as to be surroundedby the photogate electrode PG1. The first gate electrode TX1 is arrangedas spatially separated from the photogate electrode PG1 and the firstsemiconductor region FD1 so as to be interposed between the photogateelectrode PG1 and the first semiconductor region FD1.

The second gate electrode TX2 is disposed between the photogateelectrode PG2 (light receiving region) and the second semiconductorregion FD2. The second gate electrode TX2 is located outside the secondsemiconductor region FD2 so as to surround the second semiconductorregion FD2, and is also located inside the photogate electrode PG2 so asto be surrounded by the photogate electrode PG2. The second gateelectrode TX2 is arranged as spatially separated from the photogateelectrode PG2 and the second semiconductor region FD2 so as to beinterposed between the photogate electrode PG2 and the secondsemiconductor region FD2.

The first and second gate electrodes TX1, TX2 are approximatelypolygonal loop-shaped when viewed in a plan view. In the presentembodiment, the first and second gate electrodes TX1, TX2 arerectangular loop-shaped. Although the first and second gate electrodesTX1, TX2 are comprised of polysilicon, they may be comprised of othermaterials. The first and second gate electrodes TX1, TX2 function astransfer electrodes.

The third semiconductor region FD3 ₁ is located outside the photogateelectrode PG1 so as to surround the photogate electrode PG1. The thirdsemiconductor region FD3 ₁ is arranged as spatially separated from aregion immediately below the photogate electrode PG1. That is, the thirdsemiconductor region FD3 ₁ is disposed outside the light receivingregion so as to surround the light receiving region, and is alsoarranged as spatially separated from the light receiving region.

The third semiconductor region FD3 ₂ is located outside the photogateelectrode PG2 so as to surround the photogate electrode PG2. The thirdsemiconductor region FD3 ₂ is arranged as spatially separated from aregion immediately below the photogate electrode PG2. That is, the thirdsemiconductor region FD3 ₂ is disposed outside the light receivingregion so as to surround the light receiving region, and is alsoarranged as spatially separated from the light receiving region.

The third semiconductor regions FD3 ₁, FD3 ₂ are approximately polygonalloop-shaped when viewed in a plan view. In the present embodiment, thethird semiconductor regions FD3 ₁, FD3 ₂ are rectangular loop-shaped.Furthermore, in the present embodiment, the adjacent third semiconductorregions FD3 ₁, FD3 ₂ are formed integrally with each other. That is, thethird semiconductor region FD3 ₁ and the third semiconductor region FD3₂ share a region interposed between the photogate electrode PG1 (lightreceiving region) and the photogate electrode PG2 (light receivingregion). The third semiconductor regions FD3 ₁, FD3 ₂ function asunnecessary charge collecting regions. The third semiconductor regionsFD3 ₁, FD3 ₂ are regions comprised of high-impurity concentration n-typesemiconductors, and are floating diffusion regions.

The third gate electrode TX3 ₁ is disposed between the photogateelectrode PG1 (light receiving region) and the third semiconductorregion FD3 ₁. The third gate electrode TX3 ₁ is located outside thephotogate electrode PG1 so as to surround the photogate electrode PG1,and is located inside the third semiconductor region FD3 ₁ so as to besurrounded by the third semiconductor region FD3 ₁. The third gateelectrode TX3 ₁ is arranged as spatially separated from the photogateelectrode PG1 and the third semiconductor region FD3 ₁ so as to beinterposed between the photogate electrode PG1 and the thirdsemiconductor region FD3 ₁.

The third gate electrode TX3 ₂ is disposed between the photogateelectrode PG2 (light receiving region) and the third semiconductorregion FD3 ₂. The third gate electrode TX3 ₂ is located outside thephotogate electrode PG2 so as to surround the photogate electrode PG2,and is located inside the third semiconductor region FD3 ₂ so as to besurrounded by the third semiconductor region FD3 ₂. The third gateelectrode TX3 ₂ is arranged as spatially separated from the photogateelectrode PG2 and the third semiconductor region FD3 ₂ so as to beinterposed between the photogate electrode PG2 and the thirdsemiconductor region FD3 ₂.

The third gate electrodes TX3 ₁, TX3 ₂ are approximately polygonalloop-shaped when viewed in a plan view. In the present embodiment, thethird gate electrode TX3 ₁, TX3 ₂ are rectangular loop-shaped. Althoughthe third gate electrodes TX3 ₁, TX3 ₂ are comprised of polysilicon,they may be comprised of other materials. The third gate electrodes TX3₁, TX3 ₂ function as unnecessary charge collecting gate electrodes.

The photogate electrode PG1, the first gate electrode TX1 and the thirdgate electrode TX3 ₁ are concentrically disposed around the firstsemiconductor region FD1 in the order of the first gate electrode TX1,the photogate electrode PG 1 and the third gate electrode TX3 ₁ from thefirst semiconductor region FD1 side. The photogate electrode PG2, thesecond gate electrode TX2 and the third gate electrode TX3 ₂ areconcentrically disposed around the second semiconductor region FD2 inthe order of the second gate electrode TX2, the photogate electrode PG2and the third gate electrode TX3 ₂ from the second semiconductor regionFD2 side.

The thickness/impurity concentration of each of the regions is asfollows:

-   first substrate region 1Aa of semiconductor substrate 1A: thickness    5˜700 μm/impurity concentration 1×10¹⁸˜10²⁰ cm ⁻³-   second substrate region 1Ab of semiconductor substrate 1A: thickness    3˜50 μm/impurity concentration 1×10¹³˜10¹⁶ cm⁻³-   first and second semiconductor regions FD1, FD2: thickness 0.1˜0.4    μm/impurity concentration 1×10¹⁸˜10²⁰ cm ⁻³-   third semiconductor regions FD3 ₁, FD3 ₂: thickness 0.1˜0.4    μm/impurity concentration 1×10¹⁸˜10²⁰ cm⁻³

Contact holes (not shown) are formed through the insulating layer 1E soas to expose the surfaces of the first to third semiconductor regionsFD1, FD2, FD3 ₁, FD3 ₂ to the outside. Conductors (not shown) aredisposed in the contact holes so as to connect the first to thirdsemiconductor regions FD1, FD2, FD3 ₁, FD3 ₂ to the outside.

The light-shielding layer LI covers a region where the first to thirdgate electrodes TX1, TX2, TX3 ₁, TX3 ₂ and the first to thirdsemiconductor regions FD1, FD2, FD3 ₁, FD3 ₂ are disposed in thesemiconductor substrate 1A, and prevents light from being incident uponthe corresponding region. This can prevent unnecessary charges frombeing generated by light which is incident upon the region.

The regions corresponding to the photogate electrodes PG1, PG2 in thesemiconductor substrate 1A (regions immediately below the photogateelectrodes PG1, PG2) function as charge generating regions where chargesare generated in response to the incident light. Therefore, the chargegenerating regions are rectangular loop-shaped in response to the shapesof the photogate electrodes PG1, PG2 and the openings LI1, LI2. In therange image sensor 1, a first unit including the photogate electrode PG1(charge generating region immediately below the photogate electrode PG1)and a second unit including the photogate electrode PG2 (chargegenerating region immediately below the photogate electrode PG2) arelocated adjacent to each other. The first and second units locatedadjacent to each other form a single pixel P(m, n).

When a high level signal (positive electric potential) is supplied tothe first gate electrode TX1, a potential below the first gate electrodeTX1 becomes lower than a potential in the region immediately below thephotogate electrode PG1 in the semiconductor substrate 1A. This causesnegative charges (electrons) to be drawn toward the first gate electrodeTX1, and to be accumulated in a potential well formed by the firstsemiconductor region FD1. The first gate electrode TX1 causes a signalcharge to flow into the first semiconductor region FD1 in response tothe input signal. An n-type semiconductor contains a positively ionizeddonor and has a positive potential, so as to attract electrons. When alow level signal (for example, a ground electric potential) is suppliedto the first gate electrode TX1, a potential barrier is generated by thefirst gate electrode TX1. Therefore, the charges generated in thesemiconductor substrate 1A are not drawn into the first semiconductorregion FD1.

When a high level signal (positive electric potential) is supplied tothe second gate electrode TX2, a potential below the second gateelectrode TX2 becomes lower than a potential in the region immediatelybelow the photogate electrode PG2 in the semiconductor substrate 1A.This causes negative charges (electrons) to be drawn toward the secondgate electrode TX2, and to be accumulated in a potential well formed bythe second semiconductor region FD2. The second gate electrode TX2causes a signal charge to flow into the second semiconductor region FD2in response to the input signal. When a low level signal (for example, aground electric potential) is supplied to the second gate electrode TX2,a potential barrier is generated by the second gate electrode TX2.Therefore, the charges generated in the semiconductor substrate 1A arenot drawn into the second semiconductor region FD2.

When a high level signal (a positive electric potential) is supplied tothe third gate electrodes TX3 ₁, TX3 ₂, potentials in regionsimmediately below the third gate electrodes TX3 ₁, TX3 ₂ become lowerthan the potentials in regions immediately below the photogateelectrodes PG1, PG2 in the semiconductor substrate 1A. This causesnegative charges (electrons) to be drawn toward the third gateelectrodes TX3 ₁, TX3 ₂, and to flow into potential wells formed by thethird semiconductor regions FD3 ₁, FD3 ₂. When a low level signal (forexample, a ground electric potential) is supplied to the third gateelectrodes TX3 ₁, TX3 ₂, potential barriers are generated by the thirdgate electrodes TX3 ₁, TX3 ₂. Therefore, the charges generated in thesemiconductor substrate 1A are not drawn into the third semiconductorregions FD3 ₁, FD3 ₂. The third semiconductor regions FD3 ₁, FD3 ₂collect some of the charges generated in the charge generating region inresponse to the incidence of light as unnecessary charges.

In the range image sensor 1, charges generated in the deep portion ofthe semiconductor in response to incidence of light for projection aredrawn into the potential well provided on the light incident surface 1FTside. As a result, high-speed and accurate distance measurement ispossible.

Pulse light LD from the object, incident through the light incidentsurface 1FT of the semiconductor substrate 1A, reaches the lightreceiving region (charge generating region) disposed on the surface sideof the semiconductor substrate 1A. The charges generated in thesemiconductor substrate 1A in response to the incidence of pulse lightare transferred from each of the charge generating regions (each of theregions immediately below the photogate electrodes PG1, PG2) to regionsimmediately below the first or second gate electrode TX1, TX2 adjacentto the corresponding charge generating region. That is, when thedetection gate signals S₁, S₂ synchronized with the pulse drive signalS_(P) for the light source are alternately supplied to the first andsecond gate electrodes TX1, TX2 via the wiring substrate 10, the chargesgenerated in each charge generating region flow into a correspondingregion immediately below the first or second gate electrode TX1, TX2,and then flow therefrom to the first or second semiconductor region FD1,FD2.

The ratio of the charge quantity Q2 accumulated in the secondsemiconductor region FD2 to the total charge quantity (Q1+Q2)corresponds to the phase difference between the emitted pulse lightemitted with supply of the pulse drive signal S_(p) to the light sourceand the detected pulse light returning after reflection of the emittedpulsed light on the object H.

Although not shown in the diagrams, the range image sensor 1 is providedwith a back-gate semiconductor region for fixing the electric potentialof the semiconductor substrate 1A to a reference electric potential.

FIGS. 6 and 7 are diagrams illustrating potential profiles near thelight incident surface 1FT of the semiconductor substrate 1A forexplaining accumulation and discharge operations of charge. In FIGS. 6and 7, a downward direction is a positive potential direction. FIGS. 6and 7 illustrate the potential profiles along the line V-V of FIG. 4.

When light is incident, potentials φ_(PG1), φ_(PG2) in regionsimmediately below the photogate electrodes PG1, PG2 are set slightlyhigher than the substrate electric potential due to an electricpotential (for example, the intermediate electric potential between ahigher electric potential and a lower electric potential supplied to thefirst and second gate electrodes TX1, TX2) supplied to the photogateelectrodes PG1, PG2. In each of the diagrams, a potential φ_(TX1) in theregion immediately below the first gate electrode TX1, a potentialφ_(TX2) in the region immediately below the second gate electrode TX2,potentials φ_(TX31), φ_(TX32) in the regions immediately below the thirdgate electrodes TX3 ₁, TX3 ₂, a potential φ_(FD1) in the firstsemiconductor region FD1, a potential φ_(FD2) in the secondsemiconductor region FD2 and potentials φ_(FD31), φ_(FD32) in the thirdsemiconductor regions FD3 ₁, FD3 ₂ are illustrated.

When a high electric potential of the detection gate signal S₁ is inputto the first gate electrode TX1, the charges generated immediately belowthe photogate electrode PG1 are accumulated in the potential well of thefirst semiconductor region FD1 through the region immediately below thefirst gate electrode TX1 according to a potential gradient, as shown inFIG. 6. The charge quantity Q1 is accumulated in the potential well ofthe first semiconductor region FD1. While the detection gate signal S₁is being applied to the first gate electrode TX1, a low level electricpotential (e.g., ground electric potential) is supplied to the thirdgate electrode TX3 ₁. For this reason, the potential φ_(TX31) in theregion immediately below the third gate electrode TX3 ₁ is not lowered,so that charges do not flow into the potential well of the thirdsemiconductor region FD3 ₁.

A low level electric potential (for example, a ground electricpotential) is supplied to the second gate electrode TX2. For thisreason, the potential φ_(TX2) in the region immediately below the secondgate electrode TX2 is not lowered, and charges do not flow into thepotential well of the second semiconductor region FD2. When a positiveelectric potential is supplied to the third gate electrode TX3 ₂, thecharges generated in the charge generating region (the regionimmediately below the photogate electrode PG2) flow into the potentialwell of the third semiconductor region FD3 ₂ as the potential φ_(TX32)in the region immediately below the third gate electrode TX3 ₂ islowered. This causes charges, generated in the charge generatingregions, to be collected in the potential well of the thirdsemiconductor region FD3 ₂ as unnecessary charges. The unnecessarycharges collected in the potential well of the third semiconductorregion FD3 ₂ are discharged to the outside.

When the high electric potential of the detection gate signal S₂ isinput to the second gate electrode TX2, subsequent to the detection gatesignal S₁, the charges generated in the region immediately below thephotogate electrode PG2 are accumulated in the potential well of thesecond semiconductor region FD2 through the region immediately below thesecond gate electrode TX2 according to a potential gradient, as shown inFIG. 7. The charge quantity Q2 is accumulated in the potential well ofthe second semiconductor region FD2. While the detection gate signal S₂is being applied to the second gate electrode TX2, a low level electricpotential (for example, a ground electric potential) is supplied to thethird gate electrode TX3 ₂. For this reason, the potential φ_(TX32) inthe region immediately below the third gate electrode TX3 ₂ is notlowered, so that charges do not flow into the potential well of thethird semiconductor region FD3 ₂.

A low level electric potential (for example, a ground electricpotential) is supplied to the first gate electrode TX1. For this reason,the potential φ_(TX1) in the region immediately below the first gateelectrode TX1 is not lowered, and charges do not flow into the potentialwell of the first semiconductor region FD1. Meanwhile, when a positiveelectric potential is supplied to the third gate electrode TX3 ₁, thecharges generated in the charge generating region (the regionimmediately below the photogate electrode PG1) flow into the potentialwell of the third semiconductor region FD3 ₁ as the potential φ_(TX31)in the region immediately below the third gate electrode TX3 ₁ islowered. This causes charges, generated in the charge generatingregions, to be collected in the potential well of the thirdsemiconductor region FD3 ₁ as unnecessary charges. The unnecessarycharges collected in the potential well of the third semiconductorregion FD3 ₁ are discharged to the outside.

FIG. 8 is a schematic diagram for explaining a configuration of a pixel.

The detection gate signal S₁, which is a charge transfer signal, issupplied to the first gate electrode TX1. The detection gate signal S₂,which is a charge transfer signal, is given to the second gate electrodeTX2. That is, charge transfer signals having different phases aresupplied to the first gate electrode TX1 and the second gate electrodeTX2. Charge transfer signals S₃₁, S₃₂ are given to the third gateelectrodes TX3 ₁, TX3 ₂.

The charges generated in the charge generating region (the regionimmediately below photogate electrode PG1) flow into a potential wellconstructed by the first semiconductor region FD1 as signal chargeswhile the high level detection gate signal S₁ is supplied to the firstgate electrode TX1. The signal charges accumulated in the firstsemiconductor region FD1 are read out as an output (V_(out1))corresponding to the charge quantity Q1 from the first semiconductorregion FD1. The charges generated in the charge generating region (theregion immediately below the photogate electrode PG2) flow into apotential well constructed by the second semiconductor region FD2 assignal charges while the high level detection gate signal S₂ is suppliedto the second gate electrode TX2. The signal charges accumulated in thesecond semiconductor region FD2 are read out as an output (V_(out2))corresponding to the charge quantity Q2 from the second semiconductorregion FD2. These outputs (V_(out1), V_(out2)) correspond to theabove-described signal d′(m, n).

FIG. 9 is a timing chart of actual various signals.

The period of a single frame consists of a period for accumulation ofsignal charge (accumulation period) and a period for readout of signalcharge (readout period). With focus on a single pixel, during theaccumulation period, a signal based on the pulse drive signal S_(P) isapplied to the light source, and the detection gate signal S₁ is appliedto the first gate electrode TX1, in synchronism therewith. Furthermore,the detection gate signal S₂ having a predetermined phase difference(for example, a phase difference of 180°) with respect to the detectiongate signal S₁ is applied to the second gate electrode TX2. Prior to themeasurement of the distance, a reset signal is applied to the first andsecond semiconductor regions FD1, FD2, and charges accumulated thereinare discharged to the outside. After the reset signal is turned on andthen turned off, the pulses of the detection gate signals S₁, S₂ aresequentially applied to the first and second gate electrodes TX1, TX2,and furthermore charges are sequentially transferred in synchronizationwith the pulses. Then, the signal charges are integrated and accumulatedin the first and second semiconductor regions FD1, FD2.

Thereafter, during the readout period, the signal charges accumulated inthe first and second semiconductor regions FD1, FD2 are read out. Atthis time, the charge transfer signals S₃₁, S₃₂ applied to the thirdgate electrodes TX3 ₁, TX3 ₂ is at the high level, and thereforepositive electric potentials are supplied to the third gate electrodesTX3 ₁, TX3 ₂, whereby unnecessary charges are collected in the potentialwells of the third semiconductor regions FD3 ₁, FD3 ₂. The detectiongate signal S₁ and the charge transfer signal S₃₁ have opposite phases.The detection gate signal S₂ and the charge transfer signal S₃₂ haveopposite phases.

An electric potential V_(PG) supplied to the photogate electrodes PG1,PG2 is set lower than the electric potentials V_(TX1), V_(TX2),V_(TX31), V_(TX32). As a consequence, when the detection gate signalsS₁, S₂ are at the high level, the potentials φ_(TX1), φ_(TX2) are lowerthan the potentials φ_(PG1), φ_(PG2). When the charge transfer signalsS₃₁, S₃₂ are at the high level, the potentials φ_(TX31), φ_(TX32) arelower than the potentials φ_(PG1), φ_(PG2).

The electric potential VPG is set higher than the electric potentialyielded when the detection gate signals S₁, S₂ and the charge transfersignals S₃₁, S₃₂ are at a low level. When the detection gate signals S₁,S₂ are at the low level, the potentials φ_(TX1), φ_(TX2) are higher thanthe potentials φ_(PG1), φ_(PG2). Furthermore, when the charge transfersignals S₃₁, S₃₂ are at the low level, the potentials φ_(TX31), φ_(TX32)are higher than the potentials φ_(PG1), φ_(PG2).

As described above, in the present embodiment, the photogate electrodePG1 is disposed on the charge generating region, the first gateelectrode TX1 is disposed between the first semiconductor region FD1 andthe charge generating region, and the third gate electrode TX3 ₁ isdisposed between the charge generating region and the thirdsemiconductor region FD3 ₁. Furthermore, the photogate electrode PG2 isdisposed on the charge generating region, the second gate electrode TX2is disposed between the second semiconductor region FD2 and the chargegenerating region, and the third gate electrode TX3 ₂ is disposedbetween the charge generating region and the third semiconductor regionFD3 ₂.

When the signal charges are transferred to the first semiconductorregion FD1, a potential gradient descending from the third gateelectrode TX3 ₁ side to the first gate electrode TX1 side is formedacross regions immediately below the photogate electrode PG1, the firstgate electrode TX1 and the third gate electrode TX3 ₁. When the signalcharges are transferred to the second semiconductor region FD2, apotential gradient descending from the third gate electrode TX3 ₂ sideto the second gate electrode TX2 side is formed across regionsimmediately below the photogate electrode PG2, the second gate electrodeTX2 and the third gate electrode TX3 ₂. Accordingly, the chargesgenerated in the regions (charge generating regions) immediately belowthe photogate electrodes PG1, PG2 definitely migrate to the first andsecond semiconductor regions FD1, FD2, but find it difficult to migrateto the third semiconductor regions FD3 ₁, FD3 ₂. In particular, when thesignal charges are transferred to the first and second semiconductorregions FD1, FD2, the potentials φ_(TX31), φ_(TX32) in the regionsimmediately below the third gate electrodes TX3 ₁, TX3 ₂ are higher thanthe potentials φ_(PG1), φ_(PG2) in regions immediately below thephotogate electrodes PG1, PG2, whereby it is difficult for the chargesto migrate to the third semiconductor regions FD3 ₁, FD3 ₂. As a result,in the range image sensor 1, the transfer efficiency of the signalcharges is improved.

When the unnecessary charges are transferred to the third semiconductorregion FD3 ₁, a potential gradient descending from the first gateelectrode TX1 side to the third gate electrode TX3 ₁ side is formedacross regions immediately below the photogate electrode PG1, the firstgate electrode TX1 and the third gate electrode TX3 ₁. When theunnecessary charges are transferred to the third semiconductor regionFD3 ₂, a potential gradient descending from the second gate electrodeTX2 side to the third gate electrode TX3 ₂ side is formed across regionsimmediately below the photogate electrodes PG2, the second gateelectrode TX2 and the third gate electrode TX3 ₂. Accordingly, thecharges generated in the regions (charge generating regions) immediatelybelow the photogate electrodes PG1, PG2 definitely migrate to the thirdsemiconductor regions FD3 ₁, FD3 ₂ as unnecessary charges, but find itdifficult to migrate to the first and second semiconductor regions FD1,FD2. In particular, when signal charges are transferred to the thirdsemiconductor regions FD3 ₁, FD3 ₂, the potentials φ_(TX1), φ_(TX2) inthe regions immediately below the first and second gate electrodes TX1,TX2 are higher than the potentials φ_(PG1) and φ_(PG2) in the regionsimmediately below the photogate electrodes PG1, PG2, whereby it isdifficult for charges to migrate to the first and second semiconductorregions FD1, FD2. As a result, in the range image sensor 1, the transferefficiency of the unnecessary charges is improved.

These allow the range image sensor 1 in accordance with the presentembodiment to improve an accuracy of distance detection.

Meanwhile, in the present embodiment, the first and second semiconductorregions FD1, FD2 are located on the inside of the photogate electrodesPG1, PG2, and areas of the first and second semiconductor regions FD1,FD2 set smaller than areas of the photogate electrodes PG1, PG2. Forthis reason, the areas of the first and second semiconductor regionsFD1, FD2 are considerably reduced compared to areas of regions which cantransfer charges to the first and second semiconductor regions FD1, FD2in the regions (charge generating regions) immediately below thephotogate electrodes PG1, PG2. Charges (the charge quantities Q1, Q2)transferred to and accumulated in the first and second semiconductorregions FD1, FD2 generate their respective voltage changes (ΔV)represented by the following relational expressions according to thecapacitance (Cfd) of the first and second semiconductor regions FD1,FD2.

ΔV=Q1/Cfd

ΔV=Q2/Cfd

Therefore, as the areas of the first and second semiconductor regionsFD1, FD2 are reduced, the capacitance (Cfd) of the first and secondsemiconductor regions FD1, FD2 are reduced, thereby generating a greatervoltage change (ΔV). That is, a charge voltage conversion gainincreases. As a result, high sensitivity of the range image sensor 1 canbe achieved.

The first gate electrode TX1 surrounds the entire periphery of the firstsemiconductor region FD1. The second gate electrode TX2 surrounds theentire periphery of the second semiconductor region FD2. For thisreason, the signal charges are collected in the first and secondsemiconductor regions FD1, FD2 from all directions of the first andsecond semiconductor regions FD1, FD2. As a result, the area efficiency(aperture ratio) of the imaging region can be improved.

The third semiconductor regions FD3 ₁, FD3 ₂ surround the entireperipheries of the charge generating regions (photogate electrodes PG1,PG2). This separates charge generating regions, whereby it is feasibleto suppress an occurrence of cross talk. Furthermore, adjacent chargegenerating regions are formed as spatially separated from each other,and the third semiconductor regions FD3 ₁, FD3 ₂ are located between theadjacent charge generating regions. For this reason, the unnecessarycharges definitely migrate to the third semiconductor regions FD3 ₁, FD3₂, and therefore the transfer efficiency of the unnecessary charges canbe further improved.

In the present embodiment, the adjacent third semiconductor regions FD3₁, FD3 ₂ are formed integrally with each other. This reduces thedistance between the adjacent charge generating regions, therebyincreasing the usage efficiency of the sensor area. As a result, aspatial resolution can be improved.

Next, referring to FIGS. 10 to 20, the configuration of the range imagesensor 1 according to a modification example of the present embodimentwill be described.

In present modification example shown in FIG. 10, shapes of thephotogate electrodes PG1, PG2, the third gate electrodes TX3 ₁, TX3 ₂and the third semiconductor regions FD3 ₁, FD3 ₂ and an arrangement ofeach unit including the photogate electrodes PG1, PG2 are different fromthose of the above-described embodiment. FIG. 10 is a schematic diagramfor explaining a configuration of pixels in a range image sensor inaccordance with the modified example.

The inner contours of the photogate electrodes PG1, PG2 arerectangle-shaped (in detail, square-shaped), and the outer contoursthereof are octagon-shaped. The third gate electrodes TX3 ₁, TX3 ₂ andthe third semiconductor regions FD3 ₁, FD3 ₂ are octagonal loop-shaped.A plurality of first semiconductor regions (in present modificationexample, four first semiconductor regions) FD1 are disposed at thevertices of imaginary polygons (in present modification example,squares). The second semiconductor region FD2 is disposed at the centerof a square whose vertices are formed by the first semiconductor regionsFD1. The imaginary polygons may be triangles or polygons with five ormore vertices, other than squares.

In present modification example, in regard to a single second unitincluding the photogate electrode PG2 (charge generating regionimmediately below photogate electrode PG2), a plurality of first units(in present modification example, four first units) including thephotogate electrodes PG1 (charge generating regions immediately belowthe photogate electrodes PG1) is disposed adjacent to each other. Onefirst unit including the photogate electrode PG1 constitutes one pixelP(m, n), along with one second unit including the photogate electrodePG2. That is, in FIG. 10, four first units and one second unitconstitute four pixels P(m, n), P(m, n+1), P(m+1, n), and P (m+1, n+1).In the present variation, this can increase the usage efficiency of thesensor area and therefore improve the spatial resolution.

In a modification example shown in FIG. 11, a plurality of first unitsincluding the photogate electrodes PG1 and a plurality of second unitsincluding the photogate electrodes PG2 are alternately arranged in rowand column directions. FIG. 11 is a schematic diagram illustrating aconfiguration of pixels of a range image sensor according to the presentvariation.

In regard to one first unit, the one first unit constitutes one pixelP(m, n), along with each of a plurality of adjacent second units.

In the same way, in regard to one second unit, the one second unitconstitutes one pixel P(m, n), along with each of a plurality ofadjacent first units. That is, in FIG. 11, eight first units and eightsecond units constitute 24 pixels P(m, n). In the present variation,this can increase the usage efficiency of the sensor area and thereforeimprove the spatial resolution.

In a modification example shown in FIG. 12, shapes of the photogateelectrodes PG1, PG2, the first and second gate electrodes TX1, TX2, thethird gate electrodes TX3 ₁, TX3 ₂, the first and second semiconductorregions FD1, FD2, and third semiconductor regions FD3 ₁, FD3 ₂ aredifferent from those of the above-described embodiment. FIG. 12 is aschematic diagram for explaining a configuration of a pixel in a rangeimage sensor in accordance with the modified example.

The first and second semiconductor regions FD1, FD2 are circular-shaped.The photogate electrodes PG1, PG2, the first and second gate electrodesTX1, TX2, the third gate electrodes TX3 ₁, TX3 ₂, and the thirdsemiconductor regions FD3 ₁, FD3 ₂ are circular loop-shaped.

In a modification example shown in FIGS. 13 and 14, shapes of thephotogate electrode PG, the third gate electrode TX3 and the thirdsemiconductor region FD3 are different from those of the above-describedembodiment. FIG. 13 is a schematic diagram for explaining aconfiguration of a pixel in a range image sensor in accordance with themodified example. FIG. 14 is a diagram illustrating a cross-sectionalconfiguration along line XIV-XIV in FIG. 13.

The range image sensor according to the present modification example isprovided with, in each pixel P(m, n), one photogate electrode PG, thefirst and second gate electrodes TX1, TX2, one third gate electrode TX3,the first and second semiconductor regions FD1, FD2, and one thirdsemiconductor region FD3.

The photogate electrode PG has a form in which the photogate electrodePG1 and photogate electrode PG2 of the above-described embodiment areformed integrally with each other. That is, the photogate electrode PGis shared by the first unit (a unit including the first semiconductorregion FD1) and the second unit (a unit including the secondsemiconductor region FD2). This causes the charge generating regions ofthe adjacent first and second units to be formed integrally with eachother.

The third semiconductor region FD3 is disposed outside the photogateelectrode PG so as to surround the photogate electrode PG. The thirdsemiconductor region FD3 is arranged as spatially separated from aregion immediately below the photogate electrode PG. That is, the thirdsemiconductor region FD3 is disposed outside the light receiving regionso as to surround the light receiving region, and is also arranged asspatially separated from the light receiving region. The thirdsemiconductor region FD3 is rectangular loop-shaped when viewed in aplan view.

The third gate electrode TX3 is disposed between the photogate electrodePG and the third semiconductor region FD3. The third gate electrode TX3is located outside the photogate electrode PG so as to surround thephotogate electrode PG, and is also located inside the thirdsemiconductor region FD3 so as to be surrounded by the thirdsemiconductor region FD3. The third gate electrode TX3 is arranged asspatially separated from the photogate electrode PG and the thirdsemiconductor region FD3 so as to be interposed between the photogateelectrode PG and the third semiconductor region FD3. The third gateelectrode TX3 is rectangular loop-shaped when viewed in a plan view.

FIG. 15 is a timing chart of various signals in the modification exampleshown in FIGS. 13 and 14. FIGS. 16 and 17 are diagrams illustratingpotential profiles for explaining an accumulation operation of signalcharges. FIG. 18 is a diagram illustrating a potential profile forexplaining a discharge operation of unnecessary charges.

In present modification example, when detection gate signals S₁, S₂applied to the first and second gate electrodes TX1, TX2 are at a lowlevel, a charge transfer signal S₃ applied to the third gate electrodeTX3 is set to a high level, as shown in FIG. 15.

As shown in FIG. 16, when a high level signal (positive electricpotential) is supplied to the first gate electrode TX1, a potentialφ_(TX1) below the first gate electrode TX1 becomes lower than apotential φ_(PG) in a region immediately below the photogate electrodePG in the semiconductor substrate 1A. As a consequence, negative charges(electrons) are drawn toward the first gate electrode TX1, so as to beaccumulated in a potential well formed by the first semiconductor regionFD1. At this time, when a low level signal (for example, a groundelectric potential) is supplied to the second gate electrode TX2, apotential barrier is generated by the second gate electrode TX2.Therefore, the charges generated in the semiconductor substrate 1A arenot drawn into the second semiconductor region FD2.

As shown in FIG. 17, when a high level signal is supplied to the secondgate electrode TX2, a potential φ_(TX2) below the second gate electrodeTX2 becomes lower than the potential φ_(PG) in the region immediatelybelow the photogate electrode PG in the semiconductor substrate 1A. As aconsequence, negative charges (electrons) are drawn toward the secondgate electrode TX2, so as to be accumulated in a potential well formedby the second semiconductor region FD2. When a low level signal issupplied to the first gate electrode TX1, a potential barrier isgenerated by the first gate electrode TX1. Therefore, the chargesgenerated in the semiconductor substrate 1A are not drawn into the firstsemiconductor region FD1.

While the detection gate signal S₁ is being applied to the first gateelectrode TX1 and the detection gate signal S₂ is being applied to thesecond gate electrode TX2, a low level signal is supplied to the thirdgate electrode TX3. For this reason, a potential φ_(TX3) in a regionimmediately below the third gate electrode TX3 is not lowered, andcharges do not flow into the potential well of the third semiconductorregion FD3.

As shown in FIG. 18, when a high level signal is supplied to the thirdgate electrode TX3, the potential φ_(TX3) in the region immediatelybelow the third gate electrode TX3 becomes lower than the potentialφ_(PG) in the region immediately below the photogate electrode PG in thesemiconductor substrate 1A. As a consequence, negative charges(electrons) are drawn toward the third gate electrode TX3, so as to becollected in the potential well formed by the third semiconductor regionFD3.

In the present modification example, charge generating regions areexpanded relative to the first and second semiconductor regions FD1,FD2, and therefore there is an increase in the signal charges moving tothe first and second semiconductor regions FD1, FD2. As a result, thetransfer efficiency of the signal charges can be further improved.

A modification example shown in FIG. 19 is different from theabove-described embodiment in that one unit including the photogateelectrode PG constitutes a pixel P(m, n). FIG. 19 is a schematic diagramfor explaining a configuration of a pixel of a range image sensoraccording to the modification example.

The range image sensor according to the present modification example isprovided with, in each pixel P(m, n), the photogate electrode PG, thefirst gate electrode TX1, the third gate electrode TX3, the firstsemiconductor region FD1, and the third semiconductor region FD3. Theconfiguration of one unit which constitutes each pixel P(m, n) is thesame as that of the first unit (or second unit) of the above-describedembodiment.

FIG. 20 is a timing chart of various signals in the modification exampleshown in FIG. 19. As shown in FIG. 20, the detection gate signal S₁applied to the first gate electrode TX1 is intermittently given a phaseshift at a predetermined timing. In the present modification example,the detection gate signal S₁ is given a phase shift of 180° at a timingof 180°. The detection gate signal S₁ is synchronized with the pulsedrive signal S_(P) at a timing of 0°, and has a phase difference of 180°with respect to the pulse drive signal S_(P) at a timing of 180°. Thephases of the detection gate signal S₁ and the charge transfer signal S₃are opposite.

In the present modification example, signal charges accumulated in thefirst semiconductor region FD1 are read out as an output (V_(out1)) fromthe first semiconductor region FD1 at a timing of 0°, and signal chargesaccumulated in the first semiconductor region FD 1 are read out as anoutput (V_(out2)) from the first semiconductor region FD1 at a timing of180°. These outputs (V_(out1), V_(out2)) correspond to theabove-described signal d′(m, n). One unit including the photogateelectrode PG (the charge generating region immediately below thephotogate electrode PG) corresponds to one pixel, and the distance iscalculated based on outputs from the same pixel. For this reason, thisconfiguration can reduce the deviation in the calculation of thedistance compared to a configuration in which a plurality of unitscorresponds to one pixel. Furthermore, this configuration can increasethe usage efficiency of the sensor area and therefore improve thespatial resolution.

The detection gate signal S₁ may be given a phase shift of 90° at atiming of 90°, a phase shift of 180° at a timing of 180°, and a phaseshift of 270° at a timing of 270°. In this case, signal chargesaccumulated in the first semiconductor region FD1 are read out asoutputs from the first semiconductor region FD1 at a timing of 0°, 90°,180°, and 270°, and the distance is calculated based on these outputs.

The above described the preferred embodiments of the present invention,but it should be noted that the present invention is not always limitedto the above embodiments but can be modified in many ways withoutdeparting from the scope and spirit of the invention.

The range image sensor 1 may be a back-illuminated type range imagesensor, as shown in FIGS. 21 and 22. The semiconductor substrate 1A isthinned from the back surface 1BK side so as to achieve a desiredthickness. As a consequence, the first substrate region 1Aa is removed,so that the second substrate region 1Ab is exposed.

The charge generating region where charges are generated in response toincident light may be constituted of a photodiode (for example, animplanted photodiode or the like). The range image sensor 1 is notlimited to a configuration in which pixels P(m, n) are disposed in atwo-dimensional arrangement, but may have a configuration in whichpixels P(m, n) are disposed in a one-dimensional arrangement.

The p- and n-type conductions in the range image sensor 1 in accordancewith the above-mentioned embodiment are interchangeable.

From the invention thus described, it will be obvious that the inventionmay be varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedfor inclusion within the scope of the following claims.

What is claimed is:
 1. A range sensor comprising: a charge generatingregion configured to generate charges in response to incident light; asignal charge collecting region disposed inside the charge generatingregion so as to be surrounded by the charge generating region, andconfigured to collect signal charges from the charge generating region;an unnecessary charge collecting region disposed outside the chargegenerating region so as to surround the charge generating region, andconfigured to collect unnecessary charges from the charge generatingregion; a photogate electrode disposed on the charge generating region;a transfer electrode disposed between the signal charge collectingregion and the charge generating region, and configured to cause thesignal charges from the charge generating region to flow into the signalcharge collecting region in response to an input signal; and anunnecessary charge collecting gate electrode disposed between theunnecessary charge collecting region and the charge generating region,and configured to cause the unnecessary charges in the charge generatingregion to flow into the unnecessary charge collecting region in responseto an input signal.
 2. The range sensor according to claim 1, comprisinga plurality of said charge generating regions, a plurality of saidsignal charge collecting regions, a plurality of said unnecessary chargecollecting regions, a plurality of said photogate electrodes, aplurality of said transfer electrodes, and a plurality of saidunnecessary charge collecting gate electrodes; wherein the plurality ofthe transfer electrodes are supplied respective charge transfer signalshaving different phases.
 3. The range sensor according to claim 2,wherein adjacent said unnecessary charge collecting regions are formedintegrally with each other.
 4. The range sensor according to claim 2,wherein the plurality of the charge generating regions are formed asspatially separated from each other.
 5. The range sensor according toclaim 2, wherein adjacent said charge generating regions are formedintegrally with each other, and adjacent said photogate electrodes areformed integrally with each other.
 6. The range sensor according toclaim 1, wherein the transfer electrode is supplied a transfer signalwhich is intermittently given a phase shift at a predetermined timing.7. The range sensor according to claim 1, wherein the photogateelectrode, the transfer electrode and the unnecessary charge collectinggate electrode are concentrically disposed around the signal chargecollecting region in an order of the transfer electrode, the photogateelectrode, and the unnecessary charge collecting gate electrode from thesignal charge collecting region side.
 8. The range sensor according toclaim 1, wherein the signal charge collecting region isrectangular-shaped when viewed in a plan view, and the photogateelectrode, the transfer electrode, and the unnecessary charge collectinggate electrode are approximately polygonal loop-shaped.
 9. The rangesensor according to claim 1, wherein the signal charge collecting regionis circular-shaped when viewed in a plan view, and the photogateelectrode, the transfer electrode, and the unnecessary charge collectinggate electrode are approximately circular loop-shaped.
 10. A range imagesensor comprising an imaging region including a plurality of unitsdisposed in a one-dimensional or two-dimensional arrangement on asemiconductor substrate and which obtains a range image based on chargequantities output from the units, wherein each of the units is the rangesensor set forth in claim
 1. 11. The range image sensor according toclaim 10, wherein adjacent two units out of the plurality of the unitsconstitute one pixel of the imaging region.
 12. The range image sensoraccording to claim 11, wherein any one unit out of the plurality of theunits and a plurality of the units adjacent said any one unit constituteone pixel of the imaging region.
 13. The range image sensor according toclaim 10, wherein each of the units constitutes one pixel of the imagingregion.